Another superb find in 2012, almost even better than the Wild T3 I found this year; a 1950s Wild Heerbrugg T0 boussole theodolite. The T0 was Heinrich Wild's vision on the well known American transit like the 1919 K&E.

The instrument has been used for forestry works in Fruška Gora, one of the national parks on the border of Syrmia, Serbia, and Croatia (although most of it lies in Serbia).

The previous owner's grandfather, forestry engineer Vlatko Radanovic, used to work with the forestry department which used these type of instruments for all kind of measurements back in the 1960s when the national park was founded. They were however decommissioned some 20 years ago, even before Vlatko was employed.

After his retirement Radanovic took the instrument home and his grandson had the instrument recently listed on the largest on-line auction site. Two days later I was the highest bidder and the instrument made his way to the collection.

The T0 definitely is not the most accurate theodolite Wild ever produced. It has however one great advantage over all other Wild theodolites; the boussole. Thanks to it traversing could be done much quicker than by using a normal theodolite or total station as one can skip half the stations needed for the same traverse. Boussole theodolites were not uncommon, especially in the U.S.A. where most theodolites - or transits as they named them - were equipped with boussoles.

The difference with all other boussole instruments was the way they were read. Up to the Wild T0 most boussole instruments were read at two diametrical opposite sides separately, simply by estimating the position of the two ends of the needle against a circle divided in whole degrees only.

The Wild T0 however did this the same way as all other Wild instruments: by superimposing the image of two diametrically opposite parts of the compass circle on top of each other (coincidence reading). In addition to that the boussole of a Wild T0 can be locked in its position (see figure 11), by which the instrument becomes a normal theodolite.

Reading the circle could now be done in whole degrees directly on the circle, in whole arcminutes using a micrometer, and estimated a further decimal (see figure 15).

The vertical circle is levelled using a plain vial with a sensitivity of 4' per 2mm (see figure 5). The circle is read directly to 10 arcminutes and can be estimated down to a single arc minute (see figure 16).

The Wild T0 was first produced in 1932 and saw only two changes until production stopped in 1990. The model shown here is of the first series which ran until 1972 and dates from about 1956. Up to 1970 some 12,000 were produced, about double the amount of T3's (6860), a third of the amount of T2's (38,800), and a quarter of T1's (51,980) for that same period.

According to the Ahrend Prijscourant 22 a few years later, in 1962, a "T0 in metalen stolp, zonder statief, 400g..." ("T2 in metal cover, without tripod, 400g") would have cost fl.1,397.-.¹

The instrument came complete with its steel container (see figure 3), the base of which is an integral part of the instrument. Apart from the boussole this is another feature not shown on other Wild theodolites. At the underside of the base a lid can be opened to access the threaded hole for attaching the instrument to a tripod (see figure 12). Being a boussole instrument this tripod (models 2a and 2b) had to be free of iron.

The instrument is rather small, even smaller than the archetype Wild T2 (see figure 4). The telescope has a magnification power of 20 times. The reticle is different than most instruments as it has two sets of stadia hairs. Two on one side of the vertical cross-hair and two at the other. The allow distance measurements with the usual 100 and less common 50 multiplication constant (see figure 14, where the ones at the right are the ones for 100x).